/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.codec;

import java.util.Map;

import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.ResolvableType;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.lang.Nullable;
import org.springframework.util.MimeType;

/**
 * Abstract base class for {@code Decoder} implementations that can decode a
 * {@code DataBuffer} directly to the target element type.
 *
 * <p>
 * Sub-classes must implement {@link #decodeDataBuffer} to provide a way to
 * transform a {@code DataBuffer} to the target data type. The default
 * {@link #decode} implementation transforms each individual data buffer while
 * {@link #decodeToMono} applies "reduce" and transforms the aggregated buffer.
 *
 * <p>
 * Sub-classes can override {@link #decode} in order to split the input stream
 * along different boundaries (e.g. on new line characters for {@code String})
 * or always reduce to a single data buffer (e.g. {@code Resource}).
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 * @param <T>
 *            the element type
 */
public abstract class AbstractDataBufferDecoder<T> extends AbstractDecoder<T> {

    //
    // [ADD] feature for
    // see:https://github.com/spring-cloud/spring-cloud-gateway/issues/1924
    // see:https://github.com/spring-cloud/spring-cloud-gateway/issues/1793
    // see:https://github.com/spring-cloud/spring-cloud-gateway/issues/1596
    //
    private int maxInMemorySize = 300 * 1024 * 1024;

    protected AbstractDataBufferDecoder(MimeType... supportedMimeTypes) {
        super(supportedMimeTypes);
    }

    /**
     * Configure a limit on the number of bytes that can be buffered whenever
     * the input stream needs to be aggregated. This can be a result of decoding
     * to a single {@code DataBuffer}, {@link java.nio.ByteBuffer ByteBuffer},
     * {@code byte[]}, {@link org.springframework.core.io.Resource Resource},
     * {@code String}, etc. It can also occur when splitting the input stream,
     * e.g. delimited text, in which case the limit applies to data buffered
     * between delimiters.
     * <p>
     * By default this is set to 256K.
     * 
     * @param byteCount
     *            the max number of bytes to buffer, or -1 for unlimited
     * @since 5.1.11
     */
    public void setMaxInMemorySize(int byteCount) {
        this.maxInMemorySize = byteCount;
    }

    /**
     * Return the {@link #setMaxInMemorySize configured} byte count limit.
     * 
     * @since 5.1.11
     */
    public int getMaxInMemorySize() {
        return this.maxInMemorySize;
    }

    @Override
    public Flux<T> decode(
            Publisher<DataBuffer> input,
            ResolvableType elementType,
            @Nullable MimeType mimeType,
            @Nullable Map<String, Object> hints) {

        return Flux.from(input).map(buffer -> decodeDataBuffer(buffer, elementType, mimeType, hints));
    }

    @Override
    public Mono<T> decodeToMono(
            Publisher<DataBuffer> input,
            ResolvableType elementType,
            @Nullable MimeType mimeType,
            @Nullable Map<String, Object> hints) {

        return DataBufferUtils.join(input, this.maxInMemorySize)
                .map(buffer -> decodeDataBuffer(buffer, elementType, mimeType, hints));
    }

    /**
     * How to decode a {@code DataBuffer} to the target element type.
     * 
     * @deprecated as of 5.2, please implement
     *             {@link #decode(DataBuffer, ResolvableType, MimeType, Map)}
     *             instead
     */
    @Deprecated
    @Nullable
    protected T decodeDataBuffer(
            DataBuffer buffer,
            ResolvableType elementType,
            @Nullable MimeType mimeType,
            @Nullable Map<String, Object> hints) {

        return decode(buffer, elementType, mimeType, hints);
    }

}
